3;U Morris Morris: 



Similar limestone formations occur in the Upper Silurian at 

 Waratah Bay, Tyers River, Buchan River, Thomson River (between 

 Walhalla and Toongabbie). Loyola, and Delatite River near Mans- 

 field. 



According to Murray (7) all these are lithologically similar, being 

 in each case crystalline rocks, and full of crinoid stems, replaced 

 by ('aCOj. " The limestones are found in some cases to lie 

 undoubted lenticular intercalations." 



Macroscopically examined, the Cave Hill limestone is a dark 

 bluish gray, compact, crystalline, and medium grained rock. Fresh 

 specimens do not readily exhibit their organic remains, but in 

 weathered specimens, Hydrozoa, represented mainly by Favosites 

 grandipora and Heliolites. and Brachiopoda, represented especially 

 by Atrypa reticularis, occur in some cases perhaps as abundantly 

 as Crinoidea. 



Microscopic Examination. — The thin slices examined are crowdc'd 

 with fossil remains of all sizes, most of which appear to belong to 

 the Hydrozoa. Their outlines are broad and daik, probably owing 

 to impurities, but the interior is generally occupied by calcite. The 

 whole is cemented together by interstitial calcite. A grain of quartz 

 appears occasionally. Dolomite is rather common. It occurs in 

 small rusty-coloured patches, and is identified by staining. 



The signs of thermal metamorphism are entirely absent. The 

 rock owes its crystalline structure to metasomatism chiefly, and 

 possibly in some degree to stresses set up during the folding of the 

 beds. 



The Gave Hill Quart zites and Conglomerates. — This bed, which 

 is not less than 70 feet thick, overlies the limestones of Mr. 

 Mitchell's quarry conformably on the east, and forms their upper 

 limit. Owing to its superior resistance to the forces of erosion, it 

 is a prominent surface feature, forming the eastern flank of Cave 

 Hill, and a neighbouring eminence, immediately south of Cave Hill. 



At Cave Hill, the bed is a quartzite. Going south, it gradually 

 develops into a loosely consolidated conglomerate, consisting of 

 quartz pebbles set in a matrix of granular quartz. The pebbles art, 

 •easily separated from the matrix. 



Under the microscope, the quartzite is seen to consist of lounded 

 grains of quartz chiefly, and a little felspar, most of wliich show 

 i\odulose extinction. The large interstices are often occupied by a 

 fine matrix, some of which appears to liavc been produced in situ 

 by the mylonitization of the grains. Much of tiie matrix seems 

 to be a silicious cement, which is fic<iuently ferruginous. The 



